package play;

public class NullObject extends ClassObject {
    private static NullObject instance = new NullObject();

    private NullObject() {

    }


    //获取唯一的实例。
    public static NullObject instance() {
        return instance;
    }

    //在打印时输出Null。
    @Override
    public String toString() {
        return "Null";
    }

}
